Scalability and redundancy in an msc-server blade cluster

ABSTRACT

This invention relates to the field of Telecommunications, in specific to a distribution mechanism for distributing calls within a Mobile Switching Center Server Blade Cluster. In particular, a method and a corresponding distributor entity for providing scalability and redundancy in blade cluster comprising a plurality of server blades of a telecommunication system are disclosed. The method comprises the steps of receiving a message of a subscriber comprising a unique subscriber identifier determining by use of the unique subscriber identifier a first value and determining by said first value a first server blade of said blade cluster, Further, by use of the unique subscriber identifier a second value is determined and by use of said second value a second server blade of said blade cluster, whereby the first server blade is excluded from being determined.

This application claims benefit of the provisional application Ser. No.60/909,544 having the title “Scalability and redundancy in an MSC-Serverblade cluster” filed on Apr. 2, 2007.

TECHNICAL FIELD

This invention relates to the field of Telecommunications, in specificto the field of server blade technology and its use withintelecommunications. In particular, the invention relates to distributionmechanism for distributing calls within a Mobile Switching Center ServerBlade Cluster.

BACKGROUND

Mobile Services Switching Center-Servers (MSC-Servers) as they existtoday have a fixed number of processors. All mobile subscribers whichare served by an MSC-Server are processed by the same processor(s).

The fixed number of processors and the fact that all subscribers areprocessed by the same processor lead to the following disadvantages:

Capacity enhancements are possible only by replacing hardware or addingadditional nodes in the network—either one of the aforementionedcapacity enhancement is visible in the network. Such addition ofhardware, however, leads to a situation making reconfigurations in thenetwork necessary. This is on the one hand time consuming and on theother hand expensive.

A failure of a processor leads to a temporary outage for allsubscribers. In today's communication system even a temporary outage isnot acceptable, even more since some customers require specifiedavailabilities, which need to be guaranteed.

To achieve a redundant system, all processors need to be duplicated, butin this case a double failure leads to a temporary outage for allsubscribers.

Furthermore, such systems are not used in a cost-effective manner, sincethey are not used in a uniform manner.

The basic idea of the MSC-Server blade cluster (100) is to have avariable number of blades (110-1,110-2, . . . 110-(n+m−1), 110-(n+m))which offer MSC-Server functionality, so called MSC-Server blades, seeFIG. 1 a.

Each Server blade may offer a set of functions. These functions mayencompass the function of a MSC-Server, a Gateway Mobile ServicesSwitching Center (GMSC-Server) and a Visitor Location Register (VLR).All mobile subscribers which are served by a Server blade cluster (100)should be distributed over the available Server blades (110-1,110-2, . .. 110-(n+m)).

To achieve a redundant system, each subscriber can be served not only byone of the Server blades (110-1,110-2, . . . 110-(n+m)) but by two ormore.

Thus, a failure of one Server blade (110-1,110-2, . . . 110-(n+m)) canbe compensated by other Server blade(s) of the affected subscriber.

By the usage of a signaling proxy (120-1,120-2), which may communicatewith MSC-S blades (110-1,110-2, . . . 110-(n+m−1), 110-(n+m)) via anappropriate protocol such as SCTP/IP (300), the Server blades (110-1, .. . 110-(n+m−1), 110-(n+m)) may not be visible outside of the MSC-Serverblade cluster (100) and other nodes may see the MSC-Server blade cluster(100) as a single node.

The signaling proxy (120-1,120-2) may communicate via any kind ofinterface offering one or more appropriate protocols such as TimeDivision Multiplex (TDM,130), Asynchronous Transfer Mode (ATM,140),Internet Protocol (IP,150) with respective networks such as a RadioAccess Network (RAN,160) and/or a Core Network (CN,170).

Furthermore, the MSC-S Blade Cluster (100) may contain one or moreinterfaces (190-1,190-2,200-1,200-2) for Operation and MaintenanceFunctions for the Site Infrastructure and for the individual serverblades (110-1,110-2, . . . 110-(n+m)) and/or the Signaling Proxy(120-1,120-2).

SUMMARY

Solutions for the following problems will be described in the following:

-   -   how to determine the Server blades for a subscriber, and    -   how to determine which one of the Server blades has to be chosen        if a mobile subscriber needs to be processed.

The problem of determining the Server blades for a subscriber is solvedby using a stateless distributor which determines the Server blades byusing 2 or more hash-functions. The hash-functions may use a uniquesubscriber identifier such as the International Mobile SubscriberIdentity (IMSI) or the Temporary Mobile Subscriber Identity (TMSI) asinput.

In particular, this is solved by a method for providing scalability andredundancy in blade cluster of a telecommunication system, where amessage of a subscriber is received and said message comprises a uniquesubscriber identifier (IMSI). By use of said unique subscriberidentifier (IMSI) a first value (hash 1, TMSI) is determined. This firstvalue is than used to determine a first server blade of said bladecluster. Furthermore, by use of said unique subscriber identifier (IMSI)a second value (hash 2, TMSI) is determined. This second value is thanused to determine a second server blade of said blade cluster. However,for the determination of a second server blade, the previouslydetermined first server blade is excluded.

Obviously, said method can be embodied in software operable whenexecuted on a Computer.

Furthermore, said innovative idea may be embodied in a Distributorentity for providing scalability and redundancy in blade cluster of atelecommunication system. Such a Distributor entity comprises means forreceiving a message of a subscriber comprising a unique subscriberidentifier (IMSI), means for determining by use of the unique subscriberidentifier a first value (hash 1, TMSI).

The means for determining are adapted to determine by said first value(hash 1, TMSI) a first server blade of said blade cluster, and todetermine by use of the unique subscriber identifier a second value(hash 2, TMSI). Again, said means for determining are further adapted todetermine by use of said second value (hash 2, TMSI) a second serverblade of said blade cluster, whereby the first server blade is excludedfrom being determined

The problem of determining which one of the Server blades has to bechosen if a mobile subscriber needs to be processed is solved bydefining one of the Server blades as the active blade for a subscriber.The active blade will typically be used to process a subscriber. Once anactive blade is defined, it could remain the active blade until it's notable anymore to process a subscriber for a certain time, e.g. due to atemporary failure or an overload situation, etc. During that timeanother Server blade can become the active blade if the mobilesubscriber needs to be processed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a shows exemplary MSC-Server blade cluster according to theinvention,

FIG. 1 b shows exemplary a setup of a server blade of a blade clusteraccording to the invention,

FIG. 1 shows an exemplary distribution flow for a primary bladeaccording to the invention,

FIG. 2 shows an exemplary distribution flow for a further, so calledbuddy blade according to the invention,

FIG. 3 shows an exemplary message flow if a single buddy is presentaccording to a first embodiment of the invention,

FIG. 4 shows an exemplary message flow if multiple buddies are presentaccording to a second embodiment of the invention,

FIG. 5 shows an exemplary distribution for a primary blade according toa first embodiment of the invention,

FIG. 6 shows an exemplary distribution for a buddy blade according to afirst embodiment of the invention,

FIG. 7 shows an exemplary distribution for a primary blade and a firstand second buddy blade according to a second embodiment of theinvention.

DETAILED DESCRIPTION Using IMSI

In the following example an IMSI is used as an example of a uniquesubscriber identifier. The solution presented is however not limited toIMSI but is susceptible of any kind of unique subscriber identifier.

a) Stateless Distributor

In accordance with FIGS. 1, 3 and 4, a message of a subscriber isreceived comprising a unique subscriber identifier.

As mentioned above, the two or more Server blades which can process amobile subscriber are determined by using 2 or more hash-functions. Theunique subscriber identifier is used as an input to a hash-functionwhich than outputs a hash value (hash 1)

The hash-value range of the hash-function, i.e. the range of possiblevalues for all possible input values such as the unique subscriberidentifier for determining the first blade is partitioned intosub-ranges per Server blade. Thus, the unique subscriber identifier suchas the IMSI of a subscriber leads via its hash-value (hash 1) in amapping process to the first MSC-Server blade which can process thissubscriber. This blade is the so called primary blade. See FIG. 1.

The further blade server which can process a subscriber may bedetermined in the same way using a second hash-function, i.e. the uniquesubscriber identifier is used as an input to a hash-function which thanoutputs a hash value (hash 2).

The hash-value range of the hash-function, i.e. the range of possiblevalues for all possible input values such as the unique subscriberidentifier for determining the further blade is partitioned intosub-ranges per Server blade. Thus, the unique subscriber identifier suchas the IMSI of a subscriber leads via its hash-value (hash 2) in amapping process to a further MSC-Server blade which can process thissubscriber. This blade is a so called further blade or buddy blade. Inthe following, the terminology “buddy” is an alternative wording for a“further” blade server. See FIG. 2.

The used hash-functions for determining primary and one or more furtherserver blade(s) may be different or identical.

In a preferred embodiment the hash-functions are different for that thelikelihood of choosing adjacent blades is reduced.

In order to provide for a load distribution, it is foreseen to take theprocessing power into account. The processing power may reflect certainprocessing capabilities such as processing speed, memory, cache, etc.This can be dealt with in several ways of which two are explainedexemplary in the following.

For example, it is possible to choose a non-uniform hash-function whichwould map the input values on the hash-value range 0 to x in anon-uniform manner. Although in the following the hash-range isdescribed as starting at 0 and ending at x, the range depends only onthe used hash-function.

The hash-value range would than be mapped on the respective blades in analmost uniform manner, e.g. the hash value range 0 to x would besubstantially uniformly divided among the respective blades within thecluster.

Another, preferred example, is the following:

If there are blade server s with different processing power, this mayalso be reflected in different sizes of the sub-ranges.

A blade server with higher processing power may cover a largersub-range, thus it will process more subscribers. In this arrangement amore or less uniform hash-function is preferred.

Obviously, also other combinations could be use which provide for a loaddistribution.

With respect to the two—or more as described later—hash-functions usedfor determining the primary and the buddy there is a difference though.

The hash-value range of the second hash-function, which could bedifferent to the first one, should be partitioned into sub-ranges perServer blade excluding the primary blade. In doing so, it is avoidedthat the hash-functions may determine the same Server blade as primaryand buddy Server blade.

If both hash-functions would lead to the same Server blade, there wouldbe no redundancy.

The partitioning of the hash-value range to determine the secondMSC-Server blade or further blade should be done as many times as thereare MSC-Server blades foreseen for a subscriber, i.e. two or more.

The second MSC-Server blade is the so called buddy blade. See FIG. 2 foran understanding of how a buddy server blade may be determined dependingon the primary server blade and a second partitioned hash-value range.

In FIG. 2 it is shown that depending on a determined primary buddy, thesecond hash-value range addressed via a (second) hash-function can beagain partitioned into sub-ranges per Server blade excluding the primaryblade.

For a more detailed discussion, it is assumed that there are 4 serverblades within a blade cluster and each subscriber is associated to aprimary and a buddy server blade.

In the following it is assumed that as the primary blade Blade 3 isdetermined as shown in the lower portion of FIG. 2. Than the hash valuerange 2 is partitioned, into 3 portions excluding Blade 3. Because ofdifferent properties of the server blades, the sub-ranges are not equal,i.e. blade 4 covers a bigger portion of the hash value range 2 thanblades 1 and 2.

Further buddy blades, i.e. for providing more redundancy, could bedetermined by a similar process, whereby the hash-function should bepartitioned into sub-ranges per Server excluding previously determinedblades, e.g. the primary server blade and all previously for thesubscriber determined buddy blades. Such a situation is also encompassedin FIG. 1 a, where M is chosen to be greater than 1.

It should be mentioned that the primary blade is typically the bladethat usually processes a subscriber.

If it becomes unavailable and a subscriber needs to be processed duringthe unavailability, a buddy blade will process the subscriber.

The primary or buddy blade processing a subscriber is referred to in thefollowing as the active blade.

A process which can be used for returning the subscriber to its initialprimary server blade may be based on the following.

An active buddy blade will process the subscriber only until the nextlocation update of the subscriber is received.

When a location update or any other appropriate message is received onthe active buddy blade, the active buddy blade forwards the initialmessage for the location update to the primary blade (assuming that theprimary blade is available again). From that point in time the primaryblade processes the subscriber again. Such a handling offers somebenefits such as:

There is a “default blade” which “most of the time” processes asubscriber, i.e. the primary blade.

VLR data handling becomes easier, since VLR data replication may be doneonly in one direction.

Moving back to the primary blade only at location update causes leastinterference problems (e.g. subscriber data can easily be fetched fromthe HLR if needed)

The process for returning as described above could be used every timewhen an initial (included in a connection request) message with IMSI isreceived from a Radio Access Network—nodes, e.g. Base StationControllers (BSC), or service nodes, e.g. Home Location Registers (HLR).When the primary blade and a buddy blade have been determined and areavailable, it should be checked which one of the blades is the activeblade.

The function of determining the primary and further blades may beembodied in a distributor.

The distributor is an entity that in accordance with FIGS. 3 and 4comprises means for receiving an initial subscriber related message inthe Server blade cluster, and means for storing the information whichsubscriber is processed by which Server blade(s). Furthermore, thedistributor comprises means for sending messages towards other bladesand/or a signaling/proxy.

The distributor might be centralized or in a preferred embodimentdistributed onto one or more of the Server blades. In a most preferredembodiment, each blade comprises a Distributor.

By distributing the distributor, the distributor is no single point offailure or capacity bottleneck with this solution because there areseveral instances of the distributor which can be used.

Each instance of the distributor may calculate the sub-rangesindependently. However, also a centralized calculation of the sub-rangesmay be envisaged. Than, the sub-ranges need to be provided to thedistributors.

In further embodiments, the actual processing-power of the blades mightbe taken into account. If, due to a change in actual processing power, achange in the sub-ranges would be necessary, there would also arise theneed to redistribute already distributed subscribers with respect totheir primary and/or buddy blades.

b) Determining the Active blade

The information whether a Server blade is the active blade for asubscriber is stored in the VLR.

The VLR might be centralized or in a preferred embodiment distributedonto one or more of the Server blades. In a most preferred embodiment,each blade comprises a VLR together with the subscriber data.

By distributing the VLR, the VLR is no single point of failure orcapacity bottleneck with this solution because there are severalinstances of the VLR which can be used.

However, in an alternative embodiment, a single VLR for the whole Bladecluster is foreseen.

Only one of the blades can be the active blade at the same time. A bladeis set to active for a subscriber when the blade starts to process asubscriber and it was not active yet.

The distributor should send the message to the primary blade (assumingthat it's available), see FIG. 3 and FIG. 4. Then the primary bladechecks if it's the active blade for the subscriber. If it is the activeblade for the subscriber, it just starts to process the message. If it'snot the active blade for the subscriber as it is shown in FIGS. 3 and 4,it must check whether a buddy blade is the active blade. It does so bysending a message to the buddy blade as shown in FIG. 3 or to the buddyblades as shown in FIG. 4.

Obviously, the way the buddy blades are queried might be arrangeddifferently, i.e. the first buddy may as well as the primary bladedetect that it is not the active blade for the subscriber and thereforecheck whether a further buddy blade is the active blade. It does so bysending a message to the further buddy blade. Than however, the queryingbuddy blade will not report a status until it has not received a statusfrom the further buddy blade.

The buddy blade(s) answer with a message whether it is active or whetherthey are not active. If a buddy blade is active, the primary bladeforwards the previously received subscriber message to the active buddyblade and the active buddy blade processes the message.

If no buddy blade is active, the primary continues to process themessage and becomes active.

The described handling of sending a message to the primary blade insteadof letting the distributor check which of the MSC-Server blades isactive has the advantage that “most of the time” no signaling is neededbecause “most of the time” the primary blade is the active blade. Thisis also true considering the return procedure as described above.

If the distributor receives an initial subscriber related message whilethe primary blade is not available, the distributor forwards the messageimmediately to the buddy blade(s).

A Server blade may offer an “active” flag which could be removed for allor some subscribers when it's getting unavailable or loaded becauseother blade(s), i.e. the buddy blades might become the active bladeduring the unavailability.

Using TMSIs

In the following TMSI is used as a further example of a uniquesubscriber identifier. The solution presented is however not limited toTMSI but is susceptible of any kind of unique subscriber identifier.

Since subscriber related messages can contain a Temporary MobileSubscriber Identity (TMSI) instead of an IMSI, there should be also amechanism to identify the correct Server blades of a subscriber based ona received TMSI.

A TMSI could be allocated to a subscriber after having received amessage containing an IMSI. Such an allocation can be understood as amapping as performed by a hash function.

Again, the solution is to partition the whole available TMSI range intoTMSI ranges per MSC-Server blade.

Also here the processing power of the MSC-Server blades can be takeninto account as described previously. For example, a Server blade with ahigher processing power will get a larger TMSI range, see FIG. 5, whereBlade 3 and Blade 4 cover a larger sub-range of the TMSI range thanBlade 1 and Blade 2.

Whenever a primary or buddy MSC-Server blade (110-1,110-2, . . .110-(n+m−1), 110-(n+m)) starts to process a subscriber, it allocates aTMSI from its own TMSI range. Thereby, the TMSI allocated to asubscriber points directly to the active MSC-Server blade of asubscriber, which can be either the primary or the buddy blade.

To be able to find also any other Server blade which can process asubscriber if the active blade is not available, the TMSI range of eachServer blade is further divided into TMSI sub-ranges. Since the otherServer(s) blade shouldn't be the same as the active blade. otherwisethere wouldn't be any redundancy, there is as described before acorresponding TMSI sub-range for each MSC-Server blade, excluding theactive blade, see FIG. 6 and FIG. 7.

In FIG. 6 it is shown that depending on a determined primary buddy, theTMSI-value range addressed can be again partitioned into sub-ranges perServer blade excluding the primary blade.

For a more detailed discussion, it is assumed that there are 4 serverblades within a blade cluster and each subscriber is associated to aprimary and a buddy server blade.

In the following it is assumed that as the primary blade Blade 1 isdetermined as shown in FIG. 6. Than the TMSI value range is againpartitioned, into 3 portions excluding Blade 1. Hence, by mapping theTMSI range onto the remaining blades again it is possible to uniquelyidentify further blades able to process a subscriber if the primaryblade fails.

Obviously, the distribution could be done either by simply mapping theTMSI sub-range onto the remaining blades, i.e. the sub-range would bepartitioned again like for determining the primary buddy or any othersuitable function could be taken into account.

Again, the processing power could be taken into account. E.g. in FIG. 6,the TMSI sub-range of Blade 1 is mapped onto a range which is of thesame size as for the TMSI range for Blade 2, Blade 3 and Blade 4. Sincethe processing power of Blade 3 and Blade 4 is higher than the one ofBlade 1 and Blade 2, the assigned sub-ranges are bigger with respect tothe later ones.

In the following it is assumed that the processing power of Blade 3 and4 is approximately twice the processing power of Blades 1 and 2. Than asimple means could be to partition the TMSI range [x,y] into 4 portionswhereof the portion assigned to blades 1 and 2 together is ofsubstantially the same size as the portion for blade 3 or blade 4.Taking this distribution into account, it is another possibility topartition the sub-range again according to the same principle, i.e. thesub-range slice of blade 2 is half the size of the sub-range slice ofblade 3 or blade 4.

Hence, one could identify two constraints for allocating a TMSI:

-   -   A TMSI should be allocated from the TMSI range of the blade        processing a subscriber (the active blade)    -   A TMSI range is further portioned for allocating further Server        blade(s) which could process a subscriber

Taking into account, that one might prefer to have more redundancy thanin a N:1 relation, e.g. a N:2 relation where for each Server blade 2fallback plates are assigned, in the following FIG. 7 is described.

There, again the TMSI range is portioned as already shown and discussedin connection with FIG. 5. It is however in FIG. 7 assumed, that blade 3is determined as a first buddy blade. Since the goal is to have in thecase that both, the primary blade as well as the first buddy blade failsa possibility to process a subscriber another, a second buddy blade isassigned. Again, the same principle as described above is employed, i.e.the blades already assigned for a subscriber are not taken into accountwhile the sub-range is again mapped on the remaining blades. I.e. sinceblade 3 is assigned as a 1^(st) buddy blade, only blade 2 and blade 4remain available for distribution. Obviously, the distribution could bedone either by simply mapping the TMSI sub-range onto the remainingblades, i.e. the sub-range would be partitioned again like fordetermining the primary buddy or any other suitable function could betaken into account.

When a distributor receives a (initial) subscriber related message withTMSI, it should determine the active Server blade by checking the TMSIranges. If this blade is available, the distributor forwards the messageto this blade. If it's unavailable, it determines a further Server bladeby checking the TMSI sub-ranges and forwards the message to this blade(assuming that this blade is available), and so on.

If the (initial) subscriber related message is a Location UpdatingRequest, the distributor checks the old Location Area Information (LAI),i.e. the LAI that has been stored on the SIM of the Mobile Station (MS)at the last location updating before it checks the TMSI. If the old LAIis defined as own LAI in the Server blade cluster (100), the TMSI wasearlier allocated by the Server blade cluster (100) and could be usedfor distribution. Otherwise the IMSI of the subscriber is fetched fromthe MS and then the initially received message is distributed based onthe IMSI.

If a (initial) subscriber related message with TMSI is distributed tothe wrong blade (e.g. if it's a call setup but the TMSI was allocated byanother MSC-Server), a redistribution of the message will be done whenthe IMSI of the subscriber is known and trusted, e.g. afterauthentication.

In a preferred embodiment, the distribution via IMSI and a correspondingTMSI of the same subscriber results in the same Server blades of course.

The invention therefore provides in the described embodiments one ormore advantages, which can be summarized as follows:

A capacity increase/decrease is possible by simply adding/removingServer blades and (automatically) changing the partitioning of thehash-value ranges and/or TMSI ranges. Therefore, the capacity change isnot visible in the network.

A failure of a processor or a blade could be compensated by otherMSC-Server blades.

Therefore, it's not needed to duplicate the complete hardware to getredundancy.

Even double failure would not lead automatically to a temporary outageof subscribers in a system having more than one buddy blade defined.

Even in the case that only one buddy is defined and two blades are outof order, such a failure will lead only to temporary outage of a limitednumber of subscribers. The number is much lower than in traditionalset-ups since typically there are more blades available so that theprobability that a subscriber is served by exactly these bladesdecreases with an increasing number of blades.

As shown in FIG. 1 a, also the signaling proxy and the one or moreinterfaces (190,200) for Operation and Maintenance Functions for theSite Infrastructure and for the individual blades may offer redundancyby providing two (190-1,190-2,200-1,200-2) or more entities offering thefunctionality.

As discussed previously, a VLR is envisaged on each blade. However, inan alternative embodiment also a centralized VLR may be envisaged. Alsothis VLR may offer redundancy as explained above with respect to thesignaling proxy.

Typically a server blade (110) comprises a processor (410) by which thedistribution function is offered, i.e. the hash-functions may beperformed, a memory (420) offering space for a VLR database, and I/Ointerfaces (430) providing the server blades with ability to communicateeither with other blades within the same blade clusters, e.g. for datareplication reasons (VLR data replication), the signaling proxy/proxies(120,120-1,120-2) and the one or more interfaces (190,200) for Operationand Maintenance Functions for the Site Infrastructure and for theindividual blades may offer redundancy by providing two(190-1,190-2,200-1,200-2) or more entities offering the functionality.

Obviously, an I/O interface (430) could be embodied by any kind ofNetwork Interface Card or unit, while the processor (430) could be anykind of a processor including a Digital Signal Processor (DSP) orcontroller or may even be embodied in an ASIC or a FPGA Furthermore, thememory (420) may be embodied in different kind of memory either as aelectronic memory such as RAM, EPROM, EEPROM, or storage device such asany kind of optical or magnetic storage medium.

Obviously, all the methods as presented above may be embodied inhardware, software enabled hardware and software offering thecorresponding program logic itself when run on a correspondingprogrammable device, either in part or as a whole.

1. A method of providing scalability and redundancy in blade cluster ofa telecommunication system, a blade cluster acting towards the networkas a single MSC and comprising a plurality of server blades, a serverblade offering MSC-Server functionality, the method comprising the stepsof: receiving a message of a subscriber comprising a unique subscriberidentifier (IMSI); determining by use of the unique subscriberidentifier a first value (hash 1, TMSI); determining by said first valuea first server blade of said blade cluster, determining by use of theunique subscriber identifier a second value and determining by use ofsaid second value a second server blade of said blade cluster, wherebythe first server blade is excluded from being determined, said secondserver blade serving the subscriber if the said first server blade isunavailable.
 2. The method according to claim 1, wherein thedetermination of said first and second server blade comprises a mappingonto respective value ranges associated to blades of said blade cluster.3. The method according to claim 1 wherein the determination of a firstserver blade and the determination of a second server blade takes intoaccount the processing power of the available server blades.
 4. Themethod according to claim 1, wherein said unique subscriber identifieris an IMSI.
 5. The method according to claim 1, wherein the first andsecond value determined by use of the unique subscriber identifier is aTMSI.
 6. The method according to claim 1, wherein the first and secondvalue determined by use of the unique subscriber identifier is a hashvalue.
 7. The method according to claim 1 whereby said method comprisesthe steps of checking the availability of said determined first andsecond server blades and forwarding said message towards said firstserver blade if said server blade is active.
 8. The method according toclaim 7, whereby if said first server blade is inactive, said message isforwarded to said second server blade.
 9. The method according to claim7, whereby the availability of said blade server is checked via a flagindicating the availability for all or some subscribers.
 10. (canceled)11. A Distributor entity for providing scalability and redundancy in ablade cluster of a telecommunication system, the blade cluster actingtowards the network as a single MSC and comprising a plurality of serverblades, a server blade offering MSC-Server functionality, thedistributor entity comprising: receiver means for receiving a message ofa subscriber comprising a unique subscriber identifier; means fordetermining by use of the unique subscriber identifier a first value;whereby said means for determining are further adapted to determine bysaid first value a first server blade of said blade cluster, wherebysaid means for determining are further adapted to determine by use ofthe unique subscriber identifier a second value and whereby said meansfor determining are further adapted to determine by use of said secondvalue a second server blade of said blade cluster, whereby the firstserver blade is excluded from being determined, said second server bladeserving the subscriber if the said first server blade is unavailable.12. The Distributor entity according to claim 11, wherein said means fordetermining of a first and second server blade are further adapted tomap said server blades onto respective value ranges associated to bladesof said blade cluster.
 13. The Distributor entity according to claim 11,wherein said means for determining of a first and second server bladeare further adapted to take the processing power of the available serverblades into account.
 14. The Distributor entity according to claim 11,wherein said unique subscriber identifier is an IMSI.
 15. TheDistributor entity according to claim 11, wherein the first and secondvalue determined by use of the unique subscriber identifier is a TMSI.16. The Distributor entity according to claim 11, wherein the first andsecond value determined by use of the unique subscriber identifier is ahash value.
 17. The Distributor entity according to claim 11 wherebysaid means for determining are further adapted to check the availabilityof said determined first and second server blades and to forward saidmessage towards said first server blade if said server blade is active.18. The Distributor entity according to claim 17, whereby if said firstserver blade is inactive, said means for determining are further adaptedto forward said message to said second server blade.
 19. The Distributorentity according to claim 11, whereby the availability of said bladeserver is checked via a flag indicating the availability for all or somesubscribers.